The liquid crystal display device as a flat display panel is used for a large-screen TV, PC (personal computer), FA (factory automation) apparatus, OA (office automation) apparatus, a car-navigation system, a cellular phone, a smart phone, and a tablet PC, etc. As display modes of the liquid crystal display device, MVA (Multi-domain Vertical Alignment) mode and FFS (Fringe Field Switching) mode are developed. The display performance of the liquid crystal display device has been improved.
In the liquid crystal display device using the MVA mode, it is easy to obtain a uniform display with a high contrast over the large screen, and the transmissivity is comparatively higher compared with the liquid crystal display device using the FFS mode. For this reason, the liquid crystal display device in the MVA mode is commonly used from a large-screen TV to small size mobile uses, such as a cellular phone. In the liquid crystal display device using the MVA mode, an initial alignment direction of liquid crystal molecules is set to a vertical alignment direction.
By the way, in the liquid crystal display device using the MVA mode, the liquid crystal molecule is switched using n type liquid crystal material in order to make electric field act substantially in the vertical direction almost perpendicular to planes of an array substrate and a counter substrate. In a polar angle and an angle of direction which specify an alignment direction of the liquid crystal molecule, n type liquid crystal material can specify only the polar angle by electric field. For this reason, in the liquid crystal display device using the MVA mode, there is a problem that a regulation strength for alignment of the liquid crystal molecule is weak. If the regulation strength for alignment is weak, when pressure is applied, for example, from exterior, it becomes easy to generate alignment disorder of the liquid crystal molecule, which is called polling.
On the other hand, in p type liquid crystal material, the liquid crystal molecule operates in a parallel direction to the electric field, and both the polar angle and the angle of direction can be specified by electric field. Since the regulation strength for alignment of the liquid crystal molecule is large, there is a feature that the polling is not generated easily.
The liquid crystal display devices using the IPS (In-Plane Switching) mode and the FFS (Fringe Field Switching) mode use p type liquid crystal material. However, the liquid crystal display device using the IPS mode and the FFS mode has a problem that it is difficult to specify the polar angle since the liquid crystal molecules are driven in the directions along the planes of the array substrate and the counter substrate by lateral electric field. For this reason, if the regulation strength for alignment becomes weak, and, for example, the external pressure is applied, it becomes easy to generate the polling.